1. Field of the Invention
This invention relates to a machine tool in which machining is performed on a workpiece using proper working tools such as cutting tools, drills, reamers, milling cutters, or other turning tools or grinding tools, and more particularly, relates to a machine tool for multiple surface machining in which machining can be performed on a plurality of surfaces of the workpiece from a plurality of directions.
2. Description of the Prior Art
As for a machine tool which is capable to machine a top surface and left and right surfaces of a workpiece from the upward direction and the left and right directions, there are known such machines as a planomiller, or a machining center in which its machining head is changeable to a horizontal or a vertical direction. A planomiller aims to machine a relatively large workpiece, and its machine head is large and it is an extremely bulky machine. The positioning of the workpiece is made by longitudinally moving a bed bearing the workpiece. The machining of the workpiece is performed by a plurality of machining heads supported on a gate type column, with spindles extending towards the direction of the workpiece. As a result, a turning operation as well as a rotary indexing of the workpiece are difficult. Moreover, it is not desirable for machining a relative small workpiece efficiently and with high precision.
On the other hand, for example, in a special machining center, although, by providing a plurality of working tools, various machining functions can be performed, a turning operation is difficult. Also, since it is provided with an automatic tool change device, its mechanism and control become complex, and there is a problem that considerable time is consumed for tool change. Furthermore, in order to machine the workpiece from a plurality of directions, a complicated mechanism is required in order to shift the machining head between a horizontal condition and a vertical condition. As a result, there is a problem that it is not easy to maintain machining accuracy.